leslie bernstein: we have a program here at the university of southern california called the cancer surveillance program. this is one of a number of population based cancer registries around the country. a population based cancer registry defines geographic boundaries of a population and then collects information on cancer that develops in the population living within that geographic boundary. in the late 1970s, brian henderson was working at a mission hospital in new guinea when the chinese government asked him to be a consultant on cancer. dr. henderson: premiere zhou en lai had bladder cancer. in the course of his illness, he became interested in cancer and actually was a mover in getting a national register of cancer cases. a million barefoot doctors in every village in china recorded every cause of death. and then, the chinese, using relatively unsophisticated computer technology made maps of the distribution of cancer. they knew where concentrations of cancer victims were located, but not why. why was there more stomach cancer in certain parts of the country... more liver cancer in others?